On Tuesday, the Congressional Budget Office released a new study finding that the Affordable Care Act, aka Obamacare, will cause "a decline in the number of full-time-equivalent workers of about 2.0 million in 2017, rising to about 2.5 million in 2024."

That doesn't mean that Obamacare will cause 2.5 million employees to be laid off, but rather that the law will encourage the equivalent of 2.5 million full-time workers to drop out of the workforce. Here's how it will work (or rather, discourage work): Obamacare offers Medicaid to people earning up to 138 percent of the federal poverty line in states that opted into the program, and it provides subsidies to people earning above that amount, up to 400 percent of the federal poverty line. As your income increases, the subsidy decreases.

For some people, CBO notes, the incentive to reduce their hours or quit their jobs will be especially strong: "People whose income exceeds 400 percent of the FPL are ineligible for premium subsidies, and for some people those subsidies will drop abruptly to zero when income crosses that threshold."

The Obamacare subsidy cliff is so steep that if you earn just $1 above the threshold, you could end up paying anywhere from a few thousand dollars to $20,000 more for insurance, depending on your age.

Whether or not it's a good thing to encourage workers to cut their hours or quit their jobs is a matter of debate among Obamacare's supporters and opponents. Liberals point out that some people will gladly choose to work less now that they have greater economic security. But for Americans teetering on the edge of Obamacare's subsidy cliff, the decision to work more in order to earn less isn't much of a free choice at all.